Vitamin K is required for the synthesis of prothrombin, other clotting proteins, and some non-plasma proteins. The vitamin functions as a cofactor for a vitamin K-dependent carboxylase which converts protein-bound glutamyl residues to gamma-carboxyglutamic acid residues. The project will synthesize low molecular weight peptide substrate of the carboxylase which are analogs of the carboxylated region of prothrombin in an attempt to determine the specificity of the enzyme, and to probe the mechanism of action of the enzyme. An attempt will be made to synthesize peptides which serve as inhibitors of this carboxylase and use them as affinity columns in the isolation of the enzyme.